The testing and evaluation of turboprop engines requires accurate measurement of the output shaft torque. The power output of an engine in horsepower=2.pi.nT/33,000 where n=rpm of the output shaft and T=torque in ft.-lb. Mechanical power measuring devices include dynamometers which absorb energy and dissipate it as heat. This class of dynamometers often utilizes electrical generators, water brakes, compressors or fan brakes as the power absorber. The fan brake type of power absorber can be made to match the speed and torque requirements of a turboprop engine. The fan brake usually takes the form of a test club or actual flight propeller. The reason for this selection is that the power absorption device must be large in order to accommodate the relatively low speed and high torque present at the output shaft of a turboprop engine.
There is then the problem of making an accurate and repeatable measurement of the power being supplied to the fan brake by the output shaft of the engine. Measurement of torque must be both reliable and correlatable with a traceable standard as specified by the U.S. Bureau of Standards.
Our invention provides a practical and reliable solution to this torque measuring problem. Our invention accomplishes this by measuring the torque reaction forces on the engine casing. Power supplied to the propeller creates an equal and opposite reaction torque on the engine casing. The torque correlation ring serves as the engine mounting which couples the engine to the test stand. This invention makes it possible to measure output shaft torque by measuring reaction torque sensed through the engine mounting points. Torque data coupled with shaft revolutions per minute then provides a measure of output power. Note, in effect bearings are eliminated and the strain gaged beams act as flexure supports.